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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 56 |
| 4 | 441 |
| 5 | 3952 |
| 6 | 40161 |
| 7 | 442248 |
| 8 | 5288933 |
| 9 | 67100072 |
| 10 | 904408398 |
| 11 | 12777826272 |
| 12 | 189324035423 |
| 13 | 2917525618256 |
| 14 | 46754429476800 |
| 15 | 774965979970096 |
| 16 | 13279872426589125 |
| 17 | 234395323126241080 |
| 18 | 4258775222885983350 |
| 19 | 79442662095373693728 |
| 20 | 1520453631213137081776 |
[1,2,9,56,441,3952,40161,442248,5288933,67100072, 904408398,12777826272,189324035423,2917525618256, 46754429476800,774965979970096,13279872426589125, 234395323126241080,4258775222885983350, 79442662095373693728,1520453631213137081776] |